Process for chromium plating



' Patented 6, 1931 JOHN a. HANLEY, or ravmeron, it"

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-This invention relates to chromium plating ofmetallic articles and moreparti'cm la'rly to the (preparationofithesurface tub plated in or er to produce consistently there- 5 on a uniformly lustnousdeposit of chromium.

In the production'-of ornamental-rustand ticles it has chromium gives a surface which is superior to nickel or copper in its'rustand abrasionresistant qualities and which, if properly applied, gives alustrous non-tarnishable surace without bufling.

The chromium may be plated directly upon steel or other suitable base metal but since a pound of chromium may not be as cheaply deposited as a pound of nickel or copper and, inasmuch as chromium does not seem to be superior to these metals in its rust prevention ualities, the base metal would ordinarily hrst be lated with nickel or copper -or some com ination of these metals and would merely be given a final coating of chromium.

One characteristic of all chromium plat ling solutions which are .known today is that they do not plate well in the recessed portions. of the object to be plated and so may leave exposed portions. Consequently it is desirable that the top coat upon which the chromium is deposited be nickel, as the color of nickel does not strongly contrast with the color of chromium. Therefore, if we are to produce an article of lustrous finish and with a top coat of chromium we prefer to apply a thin plate of nickel, then-a plate of copper,

then a plate of nickel. The nickel surface is thenbuffed, polished, prepared for chromium plating and plated in the usual chromium plating bat In processes which have been used heretofore to roduce a hromium surface on a polished nickel article it has been the customary practice, in order to produce a' uniformly lustrous surface, to dry the article before placing it inthe chromium'plating bath and to place the article in the bath with the current turned on.

It is the object of our invention to so prepare the polished nickel surface for plating Serial No. ieaua tion' td producesuch a deposit without the necessity of drying the art1cle before insert- "it in the chromium, plating bath. abrasion-resistant surfaces on 'metallic ar:

been found that a deposit of e obtain the foregoing advantages, as well as others which will be apparent from the description and claims, by the use of the process to be described, the preferred operation being as follows:

The polished nickeled article is made the cathode in an alkaline cleanin solution, which may be a solution of caustic soda and sodium silicate, and is subsequentlyrinsed in water and dipped for a short time. in a solution of hydrochloric acid. The article is again rinsed in water and is placed immediately in the chromium plating bath. After remaining in the chromium plating thatl'ajbright deposit of chrdmium free from areas-"of inferiorlustre may be consistently obtained.- It is a further object of our invenbath for at least two seconds the current is I turned on and the article, as the cathode, is left in the plating bath until the desired thickness of deposit is obtained.

It is our theory that the success of this sequence of operations is due to the elimination of the metallic oxide which may form upon metal surfaces that have been exposed to air,

and the maintaining of-the article in that condition until the'plating operation is completed. This is done by a cathodic reduction at the metal surface, followed by anacid treatment. and the subsequent protection ofv the surface from further oxidation by maintaining it wet until the article is immersed in the chromium plating bath. The water,

two seconds is essential to the substantially complete diffusion and convection of the water film into the chromium plating solution, but that the article may be left in the bath for a longer period without detrimental results. In the operation of a commercial process, however, it would be desirablethat this time should not greatly exceed the minmum stated. 1

We have found that other basic cleaning solutions maybe substituted 'for the caustic soda and sodium silicate and also that other acids, such as sulphuricfchromic or nitricf acid, may be substituted for the hydrochloric acid solution; It isiobvious that ifchro nic acid is used for the acid dip the rinsing offthe;

article before immersion in the. chromium plating solution maybeomittedand the wet articles may be passed directly to the-plat ing tank. 1 i

The chromium plating bath" we prefer to use is a solution conta1ning'200 grams of chromic oxide, 1 gram of chromium sulphate and 7 grams of chromium carbonate per liter of solution, such a solution having a gravity of about 16 Baum, but the process is equally applicable to operation in conjunction with all chromium plating solutions containing a large percentage of chromicacid and in which plating is done under such conditions that a uniformly lustrous deposit wouldbe' produced on an article prepared for chromiumplatin by the methods used heretofore. It is t erefore obvious that our roe;

ess is applicable to chromium. platin containing various roportions o fvic ;r omic acid, chromium sul ate andchromium carbonate, and also fi baths which-may consist of chromic acid and othercompounds of use an insoluble anode. v

chromium or other suitablesubstancesr" It is also obvious to one skilled in the art that our invention may be applied toichromium plating operation in which any suit able anode is used, although we prefer to We have also found that successful results can be obtained by operating at a cathodic current" density of 100 to 150 amperes W l -r succession of comprising cleaning the article as a cathodein an alkaline bath, dipping in an acid bath, rinsing, placing immediately in a chromium platin solution and turning on the current when t e article has been in the soljution about five seconds.

2. Inaprocess for chromium'p'lating an article having .-a nickel surfacewhich has been exposed to the air,the'following sequence of steps: electrolytically cleaning the nickel surface as the cathode'infanalkaline cleaning solution, 'dippingthe' article in an acid bath,'rinsing',=fdipping the wet article into a chromium plating bath and turning onthe current after atleast two but not more'than five seconds haveela'psed, 1

3. In a rocess for chromium plating an article havinganickel surface, the succession of steps comprising, cleaning the article as a cathode in an alkaline bath, dipping in an acidbath, placing while wet in a chromium plating solution, and turnin on the'current when the article five seconds. 1 v l a 4. In aprocess for chromium plating,-.the

has been in t 'e solution about succession ofste sicomprising, electrically cleaning the artic easier-cathode in an alkaline h same-ain an acid bath, dip-i bath contain -n a high, percentage of chrom'i'c acid, allowingythe same to remain (in that ole-in a chromium; plating", i

solution at least two secondsfbe'foreturning' per square foot of article 'to be plated and at a bath temperature of from F. to F.,

' but we prefer to use a current densit of ble to depositing chromium upon a nickel about 100 amperes per'square foot and a ath vtemperature of about 100 F.

We have explained our process as applicasurface but it is apparent that such a series of steps may be advantageously used in the deposition of a superiordeposit of chromilnn upon metallic surfaces other thannilck'el.

It is further apparent that anyofth'efrinsing steps may be omitted where themechanical transfer of liquid from one tank to the other is not objectionable. Also, it is a parent that the article mightbe placed in t e chromic acid 'chromium plitting bath 7 immediately after the first rinse and allowed to remain there a somewhat longer period before turning on the current, so utilizing the acid of the bath for the acid dip.

Having thus. described our we claim is invention, what 1. In a processior chromiuiii plating, the 

